Effects of Polyhedral Oligomeric Silsesquioxane (POSS) on Thermal and Mechanical Properties of Polysiloxane Foam.

The thermal and mechanical properties of polysiloxane foam are greatly improved by the addition of acrylolsobutyl polyhedral oligomeric silsesquioxane (MA0701, hereinafter referred to as MAPOSS), which has double bonds. The morphologies and properties of the polysiloxane composite foam were characterized. The average cell diameter of the composite foams decreased, while the cell density increased with increasing MAPOSS. Meanwhile, MAPOSS can enhance thermal conductivity and thermal stability. Thermal conductivity increased by 25%, and the temperature at the maximum weight loss rate increased from 556 °C to 599 °C. In addition, MAPOSS also promoted heterogeneous nucleation by functioning as a nucleating agent, which can increase cell density to improve the mechanical properties. The compressive strength of the composite foam increased by 170% compared with that of pure foam. In the composite, MAPOSS increased the cross-linking density by acting as a physical cross-linking point and limited the movement of the segments.

Thermal insulation and stability of polysiloxane foams containing hydroxyl-terminated polydimethylsiloxanes.

An effective method was described here to improve the thermal insulation and stability of polysiloxane foam (SIF) by controlling the chain length of hydroxyl-terminated polydimethylsiloxane (OH-PDMS). A series of SIFs were prepared through foaming and cross-linking processes with different cross-linking densities. The morphology of SIF was investigated by environmental scanning electron microscopy. The results demonstrated that increasing the chain length of OH-PDMS reduced the average cell size from 932 µm to 220 µm. Cell density ranged from 4.92 × 106 cells per cm3 to 1.64 × 108 cells per cm3. The thermal insulation capability was significantly enhanced, and the SIF derived from the long-chain OH-PDMSs yielded a minimum thermal conductivity of 0.077 W mK-1. Cell size reduction and an increase in cell density were considered to be the main factors to reduce thermal conductivity. Thermal stability, which was also improved, mainly depended on the free motion rate of the polysiloxane chains and cross-linking density of the polysiloxane networks.

Improved thermal properties of epoxy resin modified with polymethyl methacrylate-microencapsulated phosphorus-nitrogen-containing flame retardant.

Epoxy resin (EP) composites with improved thermal resistance were fabricated. To solve the problem of low thermal resistance derived from phosphazene flame-retardant additives, we designed a system based on flame-retardant microcapsules P(H), with hexaphenoxycyclotriphosphazene as the core and polymethyl methacrylate as the shell. The core-shell structure was characterized and confirmed. The thermal resistance of the cured EP composites containing 1 wt% P(H) microcapsules was improved because of the increased glass transition temperatures. The P(2.75H)/EP composites can reach a limited oxygen index of 30.5% and V-1 rating in UL-94 tests. Heat and gas release rates were reduced during combustion tests. Residual images implied that the P(H) microcapsules may promote the formation of a flame-retardant char layer. Pyrolysis analysis demonstrated that the P(H) microcapsules can decompose in two procedures to produce flame-retardant gas components. Therefore, the flame-retardant mechanism involved the flame inhibition effect in the gas phase, and the charring effect in the condensed phase.